This invention relates to a capacitor for an integrated circuit and its fabrication method.
A technology for applying a high dielectric constant capacitor, such as a ferroelectric capacitor for a Random Access Memory (RAM), has been developed. In a dielectric film of the capacitor, metal oxides such as Lead Zirconate Titanate (PZT), Barium Strontium Titanate (BST) and other high dielectric constant oxides are used. In the bottom and top electrodes of the capacitor, platinum, which is hard to react with the metal oxides, is used. Between the bottom electrode and a silicon substrate, an adhesion layer of a titanium film to improve the adhesive strength between both, and a diffusion barrier layer of a titanium nitride film to prevent the adhesion layer from reacting with the bottom electrode, are formed.
A ferroelectric capacitor is generally fabricated by a method described below.
First, a titanium film, a titanium nitride film and a platinum film for a bottom electrode are deposited in layers on an insulating surface of a silicon substrate by a sputtering method using a titanium target, a titanium nitride target and a platinum target, respectively.
Next, a ferroelectric metal oxide film is deposited on the platinum film by a sputtering method or a sol-gel method, and a platinum film for a top electrode is deposited on the metal oxide film. Then, these films are finished with a predetermined shape and size of the capacitor by etching techniques to remove unnecessary portions of the films, after heat-treatment for improving the dielectric constant of the ferroelectric metal oxide film.
In the fabricated capacitor, some peelings and cracks induced by the heat-treatment are often observed between the substrate and the bottom electrode. This seems to arise because the adhesive strength between the titanium film and the titanium nitride film is not strong, because the titanium film and the titanium nitride film are not formed continuously, but are formed with separate steps.
Another capacitor, which includes a titanium dioxide film formed between the substrate and the bottom electrode instead of the titanium film and the titanium nitride film, is known in the art. The titanium dioxide film acts as both an adhesion layer and a diffusion barrier layer. The fabricating process of this capacitor is that a titanium film, a platinum film for a bottom electrode, a ferroelectric metal oxide film and a platinum film for a top electrode are deposited in layers on a substrate, and the resulting structure is heated in an oxygen gas atmosphere. As a result, the titanium film becomes a titanium dioxide film. However, in this capacitor, the adhesive strength between the substrate and the titanium dioxide film is not strong, too.
A preferred method of fabricating a capacitor for an integrated circuit, comprises a step of forming an adhesion layer of a metal over a substrate, a step of forming a diffusion barrier layer of a compound of the metal and a non-metal on the adhesion layer by annealing the adhesion layer after ion implantation of the non-metal into a surface region of the adhesion layer so as to change the metal in the surface region to the compound, a step of forming a bottom electrode layer of a noble metal on the diffusion barrier layer, a step of forming a dielectric layer of a metal oxide on the bottom electrode layer, a step of forming a top electrode layer of a conductive metal on the dielectric layer, a step of etching the top electrode layer and dielectric layer selectively, a step of etching the bottom electrode layer selectively, and a step of etching the diffusion barrier layer and adhesion layer selectively.
Another preferred method of fabricating the capacitor is that a diffusion barrier layer is formed by continuing to sputter the metal in a gas of the non-metal, which is induced at the time when a thickness of the adhesion layer reaches a predetermined thickness, instead of the applications of the ion implantation and the annealed. As a result, the diffusion barrier layer of a compound of the metal and non-metal is formed on the adhesion layer.
As pointed out in greater detail below, capacitors fabricated according to a preferred process provide the important advantage of no or very little peelings at the interface of the adhesion layer and the diffusion barrier layer, because the composition of both layers has continuity, and the adhesive strength between both layers is improved.
The invention itself, together with further advantages, will best be understood by reference to the following detailed description taken in conjunction with the accompanying drawings.